Low tunneling current MIM structure and method of manufacturing same

ABSTRACT

Disclosed herein are new MIM structures having increased capacitance with little or no tunneling current, and related methods of manufacturing the same. In one embodiment, the new MIM structure comprises a first electrode comprising a magnetic metal and having a magnetic moment aligned in a first direction, and a second electrode comprising a magnetic metal and having a magnetic moment aligned in a second direction antiparallel to the first direction. In addition, such an MIM structure comprises a dielectric layer formed between the first and second electrodes and contacting the first and second magnetic metals.

TECHNICAL FIELD

Disclosed embodiments herein relate generally to metal-insulator-metal(MIM) structures, and more particularly to new MIM structures havingincreased capacitance with little or no tunneling current, and relatedmethods of manufacturing the same.

BACKGROUND

Capacitors in electrical integrated circuits (ICs) are typicallyincorporated between the interconnect layers of a semiconductor wafer inorder to maximize the use of the space between the interconnect layers.The capacitors formed between the interconnect layers are preferably ofa metal-insulator-metal (MIM) construction, as the conductors of theinterconnect layers are metal in construction. MIM capacitors may beused to store a charge in a variety of semiconductor devices, that maybe utilized in the IC. For example, such MIM structures are one of thekey devices in radio-frequency (RF). mixed-signal integrated circuit,and DRAM application.

Conventional MIM structures consume a relatively large percentage of thesurface area of a semiconductor wafer or chip because they are typicallyconstructed as a large flat structure formed by a low dielectricconstant (k) silicon dioxide or nitride capacitor dielectric layersandwiched between upper and lower metal electrodes, positioned parallelto the wafer surface. There is an ongoing challenge to maintainsufficiently high storage capacitance despite decreasing capacitor area,since capacitance is generally a function of electrode area. In order toreduce the area of these structures, yet obtain higher capacitancedensity per unit size, the prior art has attempted a few differentapproaches.

One approach has been to replace the low-k material used for thedielectric layer with high-k materials, such as Al₂O₃, HfO, and Ta₂O₅,having a k value higher than 9. However, such high-k materials do notadhere well to the metal electrodes, which are still relatively large,thereby leading to delaminations in the MIM structures. Anotherconventional approach of increasing capacitance has been is to reducedielectric thickness. Capacitance is set forth in equation (1),

$\begin{matrix}{C = {k*\frac{A}{t}}} & (1)\end{matrix}$where C=capacitance, k=dielectric constant, A=electrode area, andt=dielectric thickness).

An even more advantageous approach for gaining capacitance (per devicesize) would be to shrink the dielectric thickness and employ a high-kmaterial simultaneously. Unfortunately, high-k materials are oftenincompatible with the idea of decreasing dielectric thickness due to theissue of leakage current. More specifically, as high-k dielectrics aremade thinner, the propensity of leakage or “tunneling” current fromelectrode to electrode across the dielectric increases. Accordingly, anMIM capacitor structure is needed that utilizes wafer area moreefficiently than conventional MIM capacitor structures, while usinghigh-k dielectrics without the detrimental effects of leakage current.

SUMMARY

Disclosed herein are new MIM structures having increased capacitancewith little or no tunneling current, and related methods ofmanufacturing the same. By preventing or drastically reducing leakagecurrent across the dielectric insulator layer, an MIM structureconstructed according to the disclosed principles allows the thicknessof that layer to be extremely thin without the high risk oftunneling/leakage current that is typically present with such thindielectrics. Such a thin dielectric layer in an MIM stack provides ahigh capacitance, despite its extremely thin size.

In one aspect, an MIM structure is provided. In one embodiment, the MIMstructure comprises a first electrode comprising a magnetic metal andhaving a magnetic moment aligned in a first direction, and a secondelectrode comprising a magnetic metal and having a magnetic momentaligned in a second direction antiparallel to the first direction. Inaddition, such an MIM structure comprises a dielectric layer formedbetween the first and second electrodes and contacting the first andsecond magnetic metals.

In another aspect, a method of manufacturing an MIM structure isprovided. In one embodiment, the method comprises forming a bottomelectrode from a magnetic metal, growing a dielectric layer on thebottom electrode, and then forming a second electrode from a magneticmetal on the dielectric layer. Such a method further provides annealingthe top and bottom electrodes to align a magnetic moment of the topelectrode in a first direction and a magnetic moment of the bottomelectrode in a second direction antiparallel to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the principles disclosure herein,and the advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates one embodiment of a metal-insulator-metal (MIM)structure constructed according to the principles disclosed herein;

FIG. 1A illustrates the spin directions of the electrodes shown in theMIM structure of FIG. 1;

FIG. 2 illustrates a graph that shows the relationship between magneticalignment and resistance;

FIG. 3 illustrates a more detailed view of one embodiment of the MIMstructure illustrated in FIG. 1; and

FIG. 4 illustrates another embodiment of an MIM structure constructedaccording to the disclosed principles, but employing two annealing stepsduring the manufacturing process.

DETAILED DESCRIPTION

Referring initially to FIG. 1, illustrated is one embodiment of ametal-insulator-metal (MIM) structure 100 constructed according to theprinciples disclosed herein. Specifically, the disclosed MIM structure100 includes a top electrode 110 and a bottom electrode 120, with ahigh-k dielectric layer 130 interposed between the top and bottomelectrodes 110, 120. As used herein, the term “high-k dielectric” meansa dielectric material having a dielectric constant of at least 9.Examples of high-k dielectric materials suitable for use with thedisclosed principles are Al₂O₃, SiO₂, Ta₂O₅, MgO and HfO, but nolimitation to any particular material is intended.

While the MIM structure 100 in FIG. 1 may appear to be similar to aconventional MIM structure because of the two electrodes surrounding adielectric layer, this MIM structure 100 is distinct from knownstructures because of the antiparallel alignment provided between thetop and bottom electrodes 110, 120. Specifically, the magnetic momentsof the top and bottom electrodes 110, 120 are aligned antiparallel toeach other when the MIM stack 100 is constructed. As discussed above,one of the primary concerns with the use of thin high-k dielectriclayers in MIM structures is the tunneling current that usually occursacross that dielectric layer. Moreover, when ferromagnetic electrodesare employed, the tunneling current is typically spin-dependenttunneling in such conventional MIM structures.

However, the disclosed principles provide for an MIM structure 100 wherethe spin directions of the electrodes 110, 120 are antiparallel to eachother, as shown in FIG. 1A. When the spin directions of the electrodes110, 120 are antiparallel (i.e., alignment of magnetic moments isantiparallel), no tunneling (or leakage) current passes across thehigh-k dielectric layer 130. This principles is set forth below inequation (2).

$\begin{matrix}{{TMR} = {\frac{I_{\uparrow \uparrow} - I_{\uparrow \downarrow}}{I_{\uparrow \downarrow}} = \frac{2P_{L}P_{R}}{1 - {P_{L}P_{R}}}}} & (2)\end{matrix}$In equation (2), parallel magnetizations are defined in equation (3),while antiparallel magnetizations are defined in equation (4).I_(↑↑)∝n_(L) ^(↑)n_(R) ^(↑)+n_(L) ^(↓)n_(R) ^(↓)  (3)I_(↑↓)∝n_(L) ^(↑)n_(R) ^(↓)+n_(L) ^(↓)n_(R) ^(↑)  (4)Also in equation (2), P_(L) and P_(R) are the spin polarizations of leftand right ferromagnets (e.g., ferromagnetic metals), and are definedrespectively in equations (5) and (6) below.

$\begin{matrix}{P_{L} = \frac{n_{L}^{\uparrow} - n_{L}^{\downarrow}}{n_{L}^{\uparrow} + n_{L}^{\downarrow}}} & (5) \\{P_{R} = \frac{n_{R}^{\uparrow} - n_{R}^{\downarrow}}{n_{R}^{\uparrow} + n_{R}^{\downarrow}}} & (6)\end{matrix}$

Turning briefly to FIG. 2, a graph is shown that illustrates therelationship between magnetic alignment and resistance. Specifically,the electrical resistance through a dielectric layer surrounded bymagnetic electrodes as the magnetic moments of the surroundingelectrodes become larger. Conversely, the resistance decreases as theybecome more parallel. Referring back to FIG. 1, in an MIM stack, theelectrical resistance of the dielectric layer 130 can therefore becontrolled by aligning the magnetic moments of the surroundingelectrodes 110, 120. As discussed in further detail below, thecomposition of electrodes 110, 120 can determine the technique used toprovide the desired antiparallel alignment.

By preventing or drastically reducing leakage current across thedielectric layer 130, an MIM structure according to the disclosedprinciples allows the thickness of that dielectric layer to be extremelythin without the high risk of tunneling that is typically present withsuch thin dielectrics. In many embodiments, the thickness of thedielectric layer 130 may be reduced to only a few Angstroms. Forexample, if Al₂O₃ is employed as the dielectric layer 130, a structure100 according to the disclosed principles may allow the dielectric layer130 to be formed with an equivalent of oxide thickness (EOT) of onlyabout 3 Angstroms. Of course, as discussed above, such a thin dielectriclayer in an MIM stack constructed in accordance with the disclosedprinciples will provide a high capacitance, despite its extremely thinsize.

FIG. 3 illustrates a more detailed view of one embodiment of the MIMstructure 100 illustrated in FIG. 1. Specifically, FIG. 3 provides moredetail on the construction of the top and bottom electrodes 110, 120 ofthe structure 100, in order to illustrate how the magnetic moments ofthese electrodes 110, 120 can be aligned antiparallel to each other, inaccordance with the disclosed principles. Specifically, a key principleof the disclosed structure is the antiparallel alignment of the magneticmoments of the portions of the top and bottom electrodes 110 c and 120 athat are adjacent to the dielectric material. In exemplary embodimentsof the disclosed structure 100, the first electrode 110 may be comprisedof two magnetic metals 110 a, 110 c surrounding a non-magnetic metalspacer 110 b. Likewise, the second electrode 120 may also be comprisedof two magnetic metals 120 a, 120 c surrounding a non-magnetic metalspacer 120 b. For either electrode 110, 120, the metal spacers 110 b,120 b may comprise copper, chromium, ruthenium, or other beneficialmetal. The upper and lower magnetic metals 110 a, 110 c, 120 a, 120 cfor each electrode 110, 120 may comprise Fe, Co, Ni, B and alloysthereof.

In this embodiment of the MIM structure 100, the magnetic moments of thelayers comprising the electrodes 110, 120 are aligned antiparallel toeach other using a single annealing process. In addition, thisembodiment provides the beneficial dielectric properties discussed abovewithout the use of antiferromagnetic materials in the structure. Morespecifically, the upper and lower magnetic metals 110 a, 110 c, 120 a,120 c for each electrode 110, 120 (respectively) are separated by theillustrated spacers 110 b, 120 b, which introduces theRuderman-Kittel-Kasuya-Yosida (“RKKY”) effect into the electrodes 110,120. A single annealing process may then be performed during manufactureof the stack 100 to set the antiparallel configuration of magnetizationbetween the top and bottom electrodes 110, 120. Although layeredferromagnetic structures such as the illustrated electrodes 110, 120utilize the RKKY effect, and thus are very sensitive to the thickness ofthe non-magnetic film, this is not a disadvantage in the disclosedstructure since a primary purpose of the disclosed principles isdecreasing layer thickness within the stack 100. Thus, sensitivity tolayer thickness due to the RKKY effect is actually used as an advantageby the disclosed technique.

FIG. 4 illustrates another embodiment of an MIM structure 200constructed according to the disclosed principles. This structure 200still includes top and bottom electrodes 210, 220, surrounding a high-kdielectric layer 230. However, instead of the electrodes 210, 220 beingconstructed of two magnetic metals surrounding a metal spacer (as in theembodiment of FIG. 3), each of the electrodes 210, 220 are comprised ofa magnetic metal 210 a, 220 a adjacent to the high-k dielectric layer230. On the other sides of the magnetic metals 210 a, 220 a areantiferromagnetic materials 210 b, 220 b. These antiferromagneticmaterials 210 b, 220 b may be comprised of FeMn, PtMn, NiMn, and alloysthereof, or any other similar material.

During the manufacturing process for the MIM structure 200 of FIG. 4, afirst annealing process is performed at a relatively high temperature(T). For example, in exemplary embodiments, the first anneal isperformed at about the high Tb (“blocking temperature”). As shown, thefirst magnetic metal 210 a has its magnetic moment polarized in aspecific direction. Then, later in the manufacturing process, a secondannealing process is performed at a relatively lower temperature (T). Inexemplary embodiments, the second anneal may be performed at about thelow Tb. In accordance with the disclosed principles, the blockingtemperature is used to set the exchange biasing direction above aspecific temperature. By applying two kinds of antiferromagents in thedisclosed structure, when the second annealing process is performed, theexchange biasing direction of the high Tb antiferromagnet will not beaffected since the annealing temperature of second annealing processwould be lower. The second magnetic metal 220 a has its magnetic momentpolarized in a specific direction that is substantially antiparallel tothe polarization of the magnetic metal 210 a in the top electrode 210.Of course, the manufacturing process may include greater or fewer stepsthan these two annealing processes, without departing from the broadscope of the disclosed principles.

As disclosed above, the MIM film structure, and methods for producingthe same, may be employed to decrease the leakage current of adielectric layer having an ultra-thin thickness for increasing thecapacitance of the MIM structure (per its size and thickness). In mostcases, the thickness of the dielectric layer may be reduced to only afew Angstroms. The disclosed technique involves an antiparallel aligningof the direction of magnetization of the ferromagnetic materials formedadjacent to the dielectric layer. Also, the tunneling current could befully suppressed by using half metal. (100% polarization). To accomplishsuch antiparallel alignment on opposing sides of the dielectric layer,only one extra processing step, an annealing process, is provided to aconventional MIM structure manufacturing process. In other embodiments,depending on the desired structure of the new MIM stack, two annealingprocesses may also be employed to accomplish the antiparallel alignment.Moreover, the disclosed principles may be employed to arrive at an MIMstructure that may be used in almost any application, including RF,mixed-mode, or DRAM applications.

While various embodiments of the disclosed principles have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Thus, the breadth and scopeof the invention(s) should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with anyclaims and their equivalents issuing from this disclosure. Furthermore,the above advantages and features are provided in described embodiments,but shall not limit the application of such issued claims to processesand structures accomplishing any or all of the above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theinvention(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” such claims should not be limited by the languagechosen under this heading to describe the so-called technical field.Further, a description of a technology in the “Background” is not to beconstrued as an admission that technology is prior art to anyinvention(s) in this disclosure. Neither is the “Brief Summary” to beconsidered as a characterization of the invention(s) set forth in issuedclaims. Furthermore, any reference in this disclosure to “invention” inthe singular should not be used to argue that there is only a singlepoint of novelty in this disclosure. Multiple inventions may be setforth according to the limitations of the multiple claims issuing fromthis disclosure, and such claims accordingly define the invention(s),and their equivalents, that are protected thereby. In all instances, thescope of such claims shall be considered on their own merits in light ofthis disclosure, but should not be constrained by the headings set forthherein.

1. A metal-insulator-metal (MIM) structure, comprising: a firstelectrode comprising a magnetized metal and having a permanent magneticmoment aligned in a first direction; a second electrode comprising amagnetized metal and having a permanent magnetic moment aligned in asecond direction antiparallel to the first direction; and a dielectriclayer formed between the first and second electrodes and contacting thefirst and second magnetized metals.
 2. An MIM structure according toclaim 1, wherein the magnetized metal is selected from the consisting ofat least one of Ni, Fe, Co, B and alloys thereof.
 3. An MIM structureaccording to claim 1, wherein the magnetized metal of the first andsecond electrodes comprises a first magnetized metal and a secondmagnetized metal separated by a magnetized metal spacer, the firstmagnetized metal contacting the dielectric layer and having a permanentmagnetic moment aligned in one of the first or second directions, andthe second magnetized metal having a permanent magnetic moment alignedin the other of the first or second directions.
 4. An MIM structureaccording to claim 3, wherein the metal spacer comprises at least oneselected from the group consisting of ruthenium, chromium, and copper.5. An MIM structure according to claim 1, wherein the first and secondelectrodes each further comprise an antiferromagnetic material formed onthe magnetized metal.
 6. An MIM structure according to claim 5, whereinthe antiferromagnetic material comprises at least one selected from thegroup consisting of PtMn, NiMn and IrMn.
 7. An MIM structure accordingto claim 5, wherein the antiferromagnetic material of the firstelectrode comprises a high Tb and the antiferromagnetic material of thesecond electrode comprises a low Tb.
 8. An MIM structure according toclaim 1, wherein the dielectric layer comprises a high-k dielectricmaterial having a dielectric constant of at least
 9. 9. An MIM structureaccording to claim 8, wherein the high-k dielectric material is selectedfrom the consisting of Al₂O₃, SiO₂, Ta₂O₅, MgO, ZrO and HfO.
 10. An MIMstructure according to claim 8, wherein the dielectric layer comprises athickness of about 3 Angstroms.
 11. A method of manufacturing ametal-insulator-metal (MIM) structure, the method comprising: forming abottom electrode from a magnetized metal; growing a dielectric layer onthe bottom electrode; forming a second electrode from a magnetized metalon the dielectric layer; annealing the top and bottom electrodes toalign a permanent magnetic moment of the top electrode in a firstdirection and a permanent magnetic moment of the bottom electrode in asecond direction antiparallel to the first direction.
 12. A methodaccording to claim 11, wherein forming the top and bottom electrodescomprises forming the top and bottom electrodes from a magnetized metalselected from the consisting of at least one of Ni, Fe, Co, B and alloysthereof.
 13. A method according to claim 11, wherein forming the top andbottom electrodes comprises forming the top and bottom electrodes by:forming a first magnetized metal, forming a metal spacer on the firstmagnetized metal, and forming a second magnetized metal on the metalspacer, wherein the first magnetized metal contacts the dielectriclayer, wherein the annealing further comprises annealing the top andbottom electrodes to align a permanent magnetic moment of the firstmagnetized metal of the top electrode in the first direction, to align apermanent magnetic moment of the first magnetized metal of the bottomelectrode in the second direction, and to align a permanent magneticmoment of the second magnetized metal of the top electrode in the seconddirection, and to align a permanent magnetic moment of the firstmagnetized metal of the bottom electrode in the first direction.
 14. Amethod according to claim 13, wherein forming a metal spacer comprisesforming metal spacer comprising at least one selected from the groupconsisting of ruthenium, chromium, and copper.
 15. A method according toclaim 11, wherein forming the top and bottom electrodes furthercomprises forming an antiferromagnetic over the magnetized metal of topand bottom electrodes, and wherein the annealing further comprisesperforming a high temperature anneal to permanently align the magneticmoment of the top electrode in the first direction, and performing a lowtemperature anneal to permanently align the magnetic moment of thebottom electrode in the second direction.
 16. A method according toclaim 15, wherein performing a high temperature anneal to permanentlyalign the magnetic moment of the top electrode in the first directioncomprises performing an anneal at high Tb, and performing a lowtemperature anneal to permanently align the magnetic moment of thebottom electrode in the second direction comprises performing an annealat low Tb.
 17. A method according to claim 15, wherein forming anantiferromagnetic comprises forming an antiferromagnetic comprising atleast one selected from the group consisting of PtMn, NiMn and IrMn. 18.A method according to claim 11, wherein growing a dielectric layercomprises growing a high-k dielectric layer having a dielectric constantof at least
 9. 19. A method according to claim 18, wherein growing adielectric layer comprises growing a high-k dielectric layer comprisinga high-k dielectric material selected from the consisting of Al₂O₃,SiO₂, Ta₂O₅, MgO, ZrO and HfO.
 20. A method according to claim 18,wherein growing a dielectric layer comprises growing a high-k dielectriclayer to a thickness of about 3 Angstroms.